Note that Longjing has been explored by China (was among the first area to be explored) but for some reason it had not been exploited. One of the reasons could be the quality/concentration ("含油气构造") of the gas content underneath. This is something China may need Japanese technology to solve.

It seems to be a pragmatic first step to test the implementation and terms for "co-development". If the model proves to be successful, the two countries will extend the agreement to a larger area, gradually, and chose the extended area based on experiences accumulated in exploring and exploiting this heptagon.

The location is probably also chosen because it is somewhere where both sides currently has accumulated little geological knowledge (hence "fair" to both sides).

One very important note is that the designated area is near the north edge of the gas field. It is as far from Diaoyu as it could be. Therefore, any resolution of Diaoyu dispute is not likely to change the demarcation of this 2700 sq km area. (However, Diaoyu has implication on the Chinese claim for Okinawa Trench because it is located on the Chinese continental shelf)

Mark Valencia had argued that recent trends means that it is possible to separate Diaoyu from East China Sea dispute. In that the EEZ can be resolved before any resolution on Diaoyu.

"The Sino-Japanese conflict has two fundamental dimensions:the sovereignty dispute over the Diaoyu (Senkaku) islands andthe delimitation of a boundary for the vast EEZ and continentalshelf of the East China Sea. Many commentators have consideredThe East China Sea Dispute 165the issues inseparable. They view settlement of the first as a necessarycondition for the second. However, this view is outdated.Recent legal developments, international adjudications, statepractice, and the ratification of the Law of the 1982 UNCLOS bythe claimants point to the possibility of separating the two issues.Islands of similar location, economic utility, and legal status tothose of the Diaoyutai/Senkakus have invariably been ignored inseabed boundary delimitations between opposite states. Thissuggests that regardless of their ultimate owner, the features willonly have a maximum 12-nautical mile territorial sea aroundthem. They will not be permitted to generate their own continentalshelf or EEZ beyond that limit. The implication of this conclusionfor the Sino-Japanese maritime conflict is that the territorialand jurisdictional issues are separable and that the latter may bedealt with before the former is finally resolved. Agreement onthe irrelevance of the Diaoyutai/Senkaku territorial dispute to,and detaching it from, the Sino-Japanese jurisdictional controversywould therefore be a major milestone on the path toward asolution. Indeed if such agreement were reached it would indicatethat a boundary ignoring these features can be negotiated."

Final Reality MMVIII (Shikasu agrees with me in much louder words of "it is impossible to send even one cubic meter of the natural gas under the East China Sea to Japan (there is a trough in the way) without sending the gas first to the coast of China via a seabed pipeline, the fight over development of the gas resources was largely about pride (hokori))